Drilling tools in this type of tool family and the airlift drilling process are known from the state of the art. When there is a removal of material according to the air-lifting process (reverse circulation), there is a column of liquid in the internal cross-section of the hollow drilling rod, which forms an extraction channel, and air is blown into this extraction channel of the drilling rod above the tool head, so a difference in pressure of the column of liquid in the drilling rod arises between the base of the bore hole and the surface because of the air rising in the drilling rod. The difference in pressure induces a velocity of flow with which the material that has been detached at the base of the bore hole is driven out through the internal cross-section of the drilling rod. The magnitude of the difference in pressure, and thereby the transporting capacity, depends among other things on the amount of air blown in per unit of time, on the depth to which it is blown in and on the lifting height. The material detached from the cutting element is suctioned up from the base through a suction opening; in the process, the suction opening can be centrally located on the bottom side of the tool head or, if the tool head has a pilot tip, for example, on a position offset from the center by around xc2xc of the diameter.
When xe2x80x9csuctioning upxe2x80x9d is being discussed here and below, it is not thereby meant that a suction pump should be installed on the drilling rod. A pump is merely involved in order to press in air under high pressure through the drilling tool into the extraction channel. The hydrostatic pressure on the base of the bore hole is, however, higher than further up in the extraction channel in the mixture that exists there of water, drilled material and air. The transport actually takes place because of the higher pressure in the area of the base of the bore hole, but there is still a lower pressure in the extraction channel, and for simplification of expression xe2x80x9csuctioning upxe2x80x9d is talked about in this sense of a junction in an area of lower pressure.
In the case of the drilling tools known from the state of the art, the suction openings are usually designed so as to be circular or oval. In the case of some of the known drilling tools, several suction openings have been arranged, instead of one, distributed over the active surface of the drilling tool, in order to be able to achieve a suctioning of the material as close as possible to each cutting element. This is necessary so that the drilled material detached by the cutting elements is transported away as quickly as possible after it is detached from the base of the bore hole, and so that the drilling tool does not ineffectively operate on a layer of detached, drilled material left behind on the base of the bore hole. The arrangement last mentioned of the suction openings on several points arranged so as to vary in a radial direction requires an expensive arrangement of pipelines to connect the suction openings to the internal cross-section of the drilling rod forming the central extraction channel.
A drilling tool is known from U.S. Pat. No. 3,951,220 in which the suction openings are designed so as to be spiral shaped, so that a flow of the scavenging liquid directed from the outside to the inside is generated. It is a disadvantage, in the case of this drilling tool, that the flow is not sufficient to take larger amounts of loosened, drilled material along with it.
The problem involved with the invention is to create a drilling tool with efficient suctioning behavior, with which the material detached by the cutting elements is nearly completely suctioned up from the base of the bore hole, without the occurrence of a repeated interaction of the cutting elements with the material that has already been detached.
This task is implemented, with regard to technology and process, by providing a process for drilling bore holes into the ground while the boring material is being removed via an air lifting process by means of a drilling tool that is provided with a drilling head. The drilling head is equipped at its lower surface with cutting elements, and its upper surface is connected to hollow drilling rods having an inner conveying channel and from whose lower surface boring material mixed with the rinsing liquid is removed via the conveying channel. The cross-flow of the rinsing liquid, flowing radially inwards and having a high flow velocity, is produced at the lower surface of the drilling tool head for the purpose of carrying along the boring material.
A cross-current of the scavenging liquid running in a radial direction towards the center of the drilling tool head is generated on the active surface of the drilling tool head during the drilling; the flow rate of the cross-current is high enough to take in the material that has been detached and take it along. In the process, a lifting effect is achieved by means of the velocity of flow, which increases on the whole the suctioning behavior at the active surface and thereby the effectiveness of the air-lifting process. Because of the rotation of the drilling tool during the drilling, the crosscurrent is moved once completely over the entire cross section of the base of the bore hole per revolution of the drilling tool, so the cutting elements interact in each case with a xe2x80x9ccleaned outxe2x80x9d bore hole base.
In order to increase the lifting effect of the cross-current, fluid currents that are directed from out of the drilling tool head in a downwards direction can be superimposed on this cross-current. The effectiveness of the suctioning is further increased with these xe2x80x9cturbulence-stylexe2x80x9d, superimposed fluid currents, because even comparatively heavy drilled material is lifted to be pulled along by the cross-current.
The task of the invention with regard to its function as an apparatus is implemented by a drilling tool for drilling bore holes into the ground while the boring material is being removed via the air lifting process. The drilling tool is equipped with a drilling head whose upper surface is connected to hollow drilling rods. The hollow drilling rods have an inner conveying channel to remove the boring material. The lower surface of the drilling head is provided with cutting elements, distributed across its cross-section, and with at least one suction opening. The suction opening is connected to the conveying channel for the boring material mixed with the rinsing liquid. The suction opening is designed as a radially-extending channel, open below, whose end located towards the center is in a fluid connection with the conveying channel.
In the case of the drilling tool in accordance with the invention, the suction opening is designed as an oblong channel that is open at the bottom and that extends in a radial direction, in which a cross-current is generated from the outside to the center of the extraction channel of the drilling rod. An opening is located on the external end of the channel, in its upper wall, through which the liquid from the area of the base of the bore hole can additionally enter, so that a higher speed of the cross-current can be achieved.
The channel is preferably closed up to the end of the drilling tool head out to the periphery. The cross-current is prevented from bringing about a xe2x80x9cbulging outxe2x80x9d of the bore hole, especially in soft stone, because of the closed design of the channel out to the periphery. In one embodiment, the outer end of the channel is radially closed.
When operating, the suction opening, designed to be channel-shaped, is guided over the entire cross section of the base of the bore hole during each revolution, and the material that has been drilled loose is transported by the cross-current through the internal cross section of the drilling rod to the surface.
In order to avoid a clogging of this opening, especially in the case of drilling at low bore hole depths or in soft stone, a tubular element that extends upwards can be provided at the opening.
According to a preferred design, the outer end of the channel is provided at its upper wall with an opening serving as an additional inlet for fluid from the area of the bore hole base, so that a higher cross-flow speed can be obtained. In order to avoid clogging of this opening, particularly when drilling at low bore hole depths or in soft rock, the opening may be provided with a pipe-shaped element extending upwards. In one embodiment, an opening serving as an inlet for the clean rinsing liquid is arranged at the outer end of the channel at the upper part of its wall. In another embodiment, the opening is provided with a pipe-shaped element extending upwards.
Equipment can be provided to feed the scavenging agent to the opening in an accelerated manner and to strengthen the cross-current.
Components that influence the flow can be arranged in the channel to improve the lifting effect, and/or the wall surfaces of the channel can be designed so as to be helix-shaped or screw-shaped, so that turbulent flow behavior can be achieved in the cross-current. In one embodiment, the channel is surrounded by walls whose side facing the inside of the channel is provided with a flow-influencing profile.
Nozzles or jets that are directed downwards and fed through an air line can additionally be installed that increase the lifting effect of the detached material by whirling it up. In one embodiment, at least one side of the channel is provided with jets, essentially directed downwards and fed by air or rinsing liquid, for the purpose of whirling-up loosened material.
In order to achieve an adequate supply of the cross-current with scavenging liquid, at least one additional supply line for the scavenging liquid and/or one additional supply line for the air can extend along the drilling rod. For special applications, the tool head can be designed in such a way that drilling is possible from out of a support pipe. In one embodiment, at least one additional air inlet pipe and/or one additional inlet pipe for the rinsing liquid is/are arranged extending along the drilling rods.
In summary, there is provided a process for drilling bore holes into the ground while the boring material is being removed via an air lifting process by means of a drilling tool that is provided with a drilling head. The drilling head is equipped at its lower surface with cutting elements, and its upper surface is connected to hollow drilling rods having an inner conveying channel. The boring material at the lower surface of the drilling head is rinsing liquid and is removed via the conveying channel. The cross-flow of the rinsing liquid, flowing radially inwards and having a high flow velocity, is produced at the lower surface of the drilling tool head for the purpose of carrying along the boring material. In one arrangement, additional flows are superimposed on the cross-flow. In another arrangement, there is provided a drilling for drilling bore holes into the ground while the boring material is being removed via an air lifting process. The drilling tool is equipped with a drilling head whose upper surface is connected to hollow drilling rods. The hollow drilling rods have an inner conveying channel to remove the boring material. The lower surface of the drilling head is provided with cutting elements, distributed across its cross-section, and with at least one suction opening. The suction opening is connected to the conveying channel for the boring material mixed with the rinsing liquid. The suction opening is designed as a radially-extending channel, open below, whose end located towards the center is in a fluid connection with the conveying channel. In still another arrangement, the outer end of the channel is radially closed. In yet another arrangement, an opening serving as an inlet for the clean rinsing liquid is arranged at the outer end of the channel at the upper part of its wall. In still yet another arrangement, the opening is provided with a pipe-shaped element extending upwards. In a further arrangement, the rinsing liquid can be passed to the opening in an accelerated way. In yet a further arrangement, components influencing the flow are arranged inside the channel. In still a further arrangement, the channel is surrounded by walls whose side facing the inside of the channel is provided with a flow-influencing profile. In still yet a further arrangement, at least one side of the channel is provided with jets essentially directed downwards and fed by air or rinsing liquid, for the purpose of whirling-up loosened material. In another arrangement, at least one additional air inlet pipe and/or one additional inlet pipe for the rinsing liquid is/are arranged extending along the drilling rods. In still another arrangement, the tool head is designed in such a way that it can be used for drilling from a supporting rod.
Further design developments and advantages of the invention are evident from the following description of three design examples, with reference to the drawing.